1. Technical Field
The present invention relates to a power supply device and a power supplying process for a computer system, and more particularly, to a power supply device for efficiently supplying power from a central power supply source to a main computer system and the monitor.
2. Background Art
Conventional personal computer systems generally consist of a main unit (which may have built-in storage devices such as floppy disks, hard disks and CD-ROM), a keyboard and a monitor. The main unit may also be connected to a printer and other peripheral devices. In normal usage, it is common for the monitor and other peripherals to be turned on and to remain on for as long as the computer is running, even though the peripherals are actually used only a small percentage of the time. A typical color video monitor, for example, may consume as such as 50 to 80 percent of the total electrical energy consumed by a personal computer (PC). If the monitor consumes valuable energy only to remain idle, not only the valuable energy resources will be wasted but the life of the monitor will decrease rapidly. Obviously, power can be conserved if the user turn the computer system off or utilizes a standby mode each time the computer system is no longer in use for an extended period. This requirement is, however, impractical. Therefore, a system should be designed to automatically conserve valuable energy resources when the computer system is not in use.
In principle, automatically saving energy by turning off the computer system is fairly easy. Portable computers such as laptop computers disclosed, for example in U.S. Pat. No. 4,980,836 for Apparatus For Reducing Computer System Power Consumption issued to Carter et al., U.S. Pat. No. 5,163,124 for Method And Apparatus For Controlling Power To Device In A Computer System issued to Yabe et al., U.S. Pat. No. 5,218,704 for Real-Time Power Conservation For Portable Computers issued to Watt, Jr. et al. and U.S. Pat. No. 5,249,298 for Battery-Initiated Touch-Sensitive Power-Up issued to Bolan et al., contain such power saving features for several years. Typically, the portable computer is invariably designed so that if there is no activity from the keyboard or from other external inputs during a specified time, the computer system is turned off or placed in a standby mode to save energy. Only minimal logic is kept active to detect when the keyboard or other external inputs are becoming active again so as to turn the computer system back on. In portable computers, this power saving feature is fairly simple to implement, since the monitor display is integrated with the computer system. However, for normal desktop personal computers in which a monitor is physically separated from the main computer unit, turning off the external monitor automatically from the main computer unit is much more difficult because most monitor systems are based on standardized data protocols such as VGA, EGA, MGA and CGA that contain no special lines or special commands to turn the power on or off.
Conventional power saving features for normal personal computers having monitors as separate items are disclosed, for example, in U.S. Pat. No. 5,059,961 for Screen Blanker For A Monitor Of A Computer System issued to Cheng, U.S. Pat. No. 5,375,245 for Apparatus For Automatically Reducing The Power Consumption Of A CRT Computer Monitor issued to Solhjell et al., U.S. Pat. No. 5,389,952 for Low-Power-Consumption Monitor Standby System issued to Kikinis, U.S. Pat. No. 5,408,668 for Method And Apparatus For Controlling The Provision Of Power To Computer Peripherals issued to Tornai, and recent U.S. Pat. No. 5,483,464 for Power Saving Apparatus For Use In Peripheral Equipment Of A Computer issued to Song and assigned to the same assignee of the present invention. Usually, the monitor is shut down during the period of inactivity with the exception of a small amount of power necessary to detect when the computer system becomes active again so as to resume operation of the monitor. Conventional personal computers, however, require separate AC power supply sources for supplying power to the main computer unit and the monitor. This requirement, as I have observed, restricts the efficiency of the power saving feature and fails to control the power supply efficiently. Moreover, using additional expensive power supply devices result in the undesirable increase of production cost.